diff --git a/sphinx/texinputs/sphinx.sty b/sphinx/texinputs/sphinx.sty
index 54e8567715..758fb9a89f 100644
--- a/sphinx/texinputs/sphinx.sty
+++ b/sphinx/texinputs/sphinx.sty
@@ -118,6 +118,10 @@
     \fancyhead[LE,RO]{{\py@HeaderFamily \@title, \py@release}}
     \renewcommand{\headrulewidth}{0.4pt}
     \renewcommand{\footrulewidth}{0.4pt}
+    % define chaptermark with \@chappos when \@chappos is available for Japanese
+    \ifx\@chappos\undefined\else
+      \def\chaptermark##1{\markboth{\@chapapp\space\thechapter\space\@chappos\space ##1}{}}
+    \fi
   }
   % Update the plain style so we get the page number & footer line,
   % but not a chapter or section title.  This is to keep the first